Infrared to visible upconversion emission in Nb₂O₅ modified tellurite glasses triply doped with rare earth ions

We report on the up-conversion emission properties of Nb₂O₅ modified tellurite glasses activated with rare earth ions in the Pr-Er-Yb, Er-Tm-Yb and Tm-Ho-Yb order. Glass samples were synthesized using the traditional melt quenching method. The synthesized samples were optically characterized using the optical absorption and up-conversion emission measurements. The band gap values of the samples for direct and indirect transitions were calculated using the absorption spectra of the samples. The up-conversion luminescence spectra of the samples were measured in the 350 to 900 nm wavelength range and three primary colors (red, green and blue) were simultaneously obtained from the samples activated with Tm-Er-Yb ions under 975 nm excitation. The dependence of the emission intensities on the pumping excitation power were investigated to make an explanation for the possible mechanisms responsible for the up-conversion emission of the samples. The color quality parameters, like CIE coordinates and color temperatures, of the obtained visible emissions, were also determined. (paper)